PSI - Issue 17

Trevor Sabiston et al. / Procedia Structural Integrity 17 (2019) 666–673 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

673

8

4. Conclusions

The modified Waterloo geometry using a 10 mm gauge width is used to produce S-N fatigue life curves of carbon fibre NCF composite materials under fully reversed loading at room temperature and 130 ℃ . It has been demonstrated through 3D DIC strain mapping that this geometry leads to a uniform strain field in the gauge length of the specimen. Through trial fatigue testing it was demonstrated that this 10 mm width specimen reduces the load required to achive a given stress level while reducing the scatter of the 6.4 mm width specimen. It was found during trial fatigue testing that CNC cutting of the specimens reduces the scatter in the results compared to waterjet cutting. The 10 mm width specimen resists buckling under compressive loads. Post mortem macroscopic analysis of the fractured specimens indicate that inter ply delamination is the primary failure mode experienced during the fatigue testing. This failure mode is confirmed using SEM analysis of the fractured region where in plane matrix cracks along with debonding of fibres in the resin rich regions between the plies is evident. Both of the S-N fatigue data sets at room temperature and 130 ℃ are well represented using a Basquin type equation to predict the safe stress amplitude for a given number of cycles. It is found that half the UCS could be used as an infinite life limit for the NCF composite material.

Acknowledgements

We would like to acknowledge Ford Motor Company for providing the material and financial support for completing this project.

References

Carvelli, V., Tomaselli, V.N., Lomov, S.V., Verpoest, I., Witzel, V., Van den Broucke, B., 2010. Fatigue and post-fatigue tensile behaviour of non crimp and unstitched carbon/epoxy composites. Composites Science and Technology 70, 2216-2224. Charalambous, G., Allegri, G., Hallett, S.R., 2015. Temperature effects on mixed mode I/II delamination under quasi-static and fatigue loading of a carbon/epoxy composite. Composites: Part A 77, 75-86. Dabayeh, A.A., Xu, R.X., Du, B.P., Topper, T.H., 1996. Fatigue of cast aluminum alloys under constant and variable-amplitude loading. International Journal of Fatigue 18, 95-104. Edgren, F., Asp, L.E., Joffe, R., 2006. Failure of NCF composites subjected to combined compression and shear loading. Composites Science and Technology 66, 2865-2877. Mouritz, A.P., Leong, K.H., Herszberg, I., 1997. A review of the effect of stitching on the in-plane mechanical properties of fibre-reinforced polymer composites. Composite Part A 28A, 979-991. Vallons, K., Zong, M., Lomov, S.V., Verpoest, I., 2007. Carbon composites based on multi-axial multi-ply stitched preforms – Part 6. Fatigue behaviour at low loads: Stiffness degradation and damage development. Composites: Part A 38, 1633-1645. Vallons, K., Lomov, S.V., Verpoest, I., 2009. Fatigue and post-fatigue behaviour of carbon/epoxy non-crimp fabric composites. Composites: Part A 40, 251-259. Vallons, K., Duque, I., Lomov, S.V., Verpoest, I., 2011. Loading direction dependence of the tensile stiffness, strength and fatigue life of biaxial carbon/epoxy NCF composites. Composites: Part A 42, 16-21.